Worldwide coal reserves are vast, over 10 trillion metric tons, but unless cleaner and cheaper ways can be found to combust coal with air into useful heat, which subsequently can be harnessed into energy and electricity using boiler/turbines systems, coal is unlikely to become an acceptable replacement for dwindling and uncertain supplies of oil and natural gas since the combustion of coal generates unwanted carbon dioxide and other undesirable products of combustion.
Atmospheric release of unwanted carbon dioxide which is a potent greenhouse gas causes negative climate changes and global warming. The collection and cleaning of this vast amount of carbon dioxide prior to atmospheric release is expensive and energy intensive. Piping of the carbon dioxide for sequestration either above ground (either for chemical production or agricultural uses) or underground is legally and economically cumbersome and uses unproven technology with unknown side implications. In addition to carbon dioxide, the combustion of coal, also produces ash (complex oxides with many unwanted and harmful elements such as arsenic and mercury contained in the coal) which causes land, water and air pollution. Furthermore, mining coal is dangerous work, coal is dirty to burn, and much of the coal in the ground is too deep or too low in quality to be mined economically or not economically feasible to extract because the seams are too “thin”. Today, less than one-sixth of the world's coal is economically and technologically accessible.